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RE: Top Rebar??

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Commentaries to ACI 318 prior to 1989 apparently noted that it was
questionable to apply the top bar factor to multiple layers of horizontal
bars in walls, but that discussion was dropped from the commentary in ACI
318-89. I don't know why. CRSI lap splice tables also used to have a
footnote stating that it may not apply to such bars, with a reference to the
318 commentary. Apparently it is not currently addressed and becomes a
"judgement" factor. 

> -----Original Message-----
> From: David Finley [mailto:pec(--nospam--at)]
> Sent: Monday, March 19, 2001 8:36 AM
> To: seaint(--nospam--at)
> Subject: Re: Top Rebar??
> The ACI 318-83 commentary has some discussion on the multiple layers
> (12.2) - I don't know how help it will be to you.
> I distinctly remember a phrase "multiple layers of 
> reinforcing in walls need
> not be considered top bars", but I am not sure if I saw that 
> in a code or in
> the general notes of some plans.
> David Finley, P.E.
> -----Original Message-----
> From: Tom.Hunt(--nospam--at) <Tom.Hunt(--nospam--at)>
> To: seaint(--nospam--at) <seaint(--nospam--at)>
> Date: Saturday, March 17, 2001 7:27 PM
> Subject: Top Rebar??
> >Speaking of seawater structures, I have received an 
> interesting plan check
> >comment.  We have designed a rather large double cell box 
> culvert with good
> >size rebar vertically and horizontally in the walls due to a 
> significant
> >surcharge from a nearby railroad.  The plan checker has 
> requested that we
> >consider all HORIZONTAL wall bars as top bars in designing 
> our splices.
> >Now I know that the code reads that top bars are those with 
> 12 inches or
> >more of fresh concrete below but I have only used this in 
> slabs and beams.
> >I reviewed several texts and did not find anything definitive.
> >
> >When I was in school I was told that the top bar reduction 
> was due to the
> >possible accumulation of micro air bubbles rising to the 
> surface.  Would
> >this apply to all the horizontal bars in a 2 foot thick by 
> 16 feet tall
> >wall??  I have been given widely different opinions on both 
> sides of the
> >issue.
> >
> >Thomas Hunt, S.E.
> >Duke/Fluor Daniel
> >
> >